Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, a conventional dual magnetic tunneling junction (DMTJ) may be used in a conventional STT-MRAM. The conventional DMTJ typically resides on a substrate. The DMTJ uses seed layer(s), may include capping layers and may include antiferromagnetic (AFM) layers to fix the magnetization of the reference layers. The conventional DMTJ includes a first reference layer, a first (main) tunneling barrier layer, a free layer, a second (secondary) tunneling barrier layer and a second free layer. The main tunneling barrier layer is between the first reference layer and free layer. The secondary tunneling barrier layer is between the second reference layer and the free layer. The secondary tunneling barrier layer is typically thinner than the main tunneling barrier layer. A bottom contact below the DMTJ and a top contact on the DMTJ may be used to drive current through the MTJ in a current-perpendicular-to-plane (CPP) direction. The reference layers and the free layer are magnetic. The magnetization of the reference layer is fixed, or pinned, in a particular direction. The free layer has a changeable magnetization. The free layer and reference layer may be a single layer or include multiple layers.
To switch the magnetization of the free layer, a current is driven in the CPP direction. When a sufficient current is driven between the top and bottom contacts in one direction, the magnetization of the free layer may switch to be parallel to the magnetization of a first reference layer. When a sufficient current is driven in the opposite direction, the magnetization of the free layer may switch to be antiparallel to that of the first reference layer. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the conventional MTJ. To reduce the switching current, the magnetizations of the reference layers are in a dual state. In other words, the magnetic moments of the reference layers are antiparallel. However, the dual state results in a reduced tunneling magnetoresistance.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. For example, a low switching current and a high signal are desired. Accordingly, what is needed is a method and system that may improve the performance of spin transfer torque based memories and the electronic devices in which such memories are used. The method and system described herein address such a need.